It is known that ends of thermoplastic filaments grouped to a tuft can be fused together by applying heat to the end of the filaments such that the ends of the filaments melt and the molten material forms a ball-like structure that connects all filaments of the tuft. Such a ball-like structure typically also has a larger diameter than the tuft and thus supports the fixation of the tuft in a carrier material that may be injection molded around the end of the tuft. The heat may be applied in various ways, e.g. by contacting the filament ends with a hot plate, by applying a stream of hot air to the ends of the filaments or by exposing the ends of the filaments to heat radiation. EP 0 676 268 A1 generally discusses the process of fusing the ends of filaments grouped into tufts by use of a hot air gun or a heating plate.
Document DE 198 53 030 A1 describes a fusing method in which a heating block, which comprises heating elements to heat the block, emits heat radiation to be received by the ends of filament tufts. The heating block comprises a channel for additional emission of hot air towards a larger sized filament tuft so that all tufts are heated within the same time amount independent on the tuft size.
Document EP 2 534 973 A2 describes a hot gas device having a multiplicity of gas nozzles for applying varying flows of hot gas towards tuft ends and an infrared radiation device comprising a plurality of infrared radiation sources each having a reflector for applying varying degrees of infrared radiation towards the tuft ends. The individual nozzles or reflectors may be arranged at consistent distances or at different distance to the tuft ends.
Document EP 0 150 785 A2 discusses a heating element that has individual heating pins for melting recesses into a tuft carrier. Further, another heating element is discussed that on one side has a hemispherical mold surface on one side of the heating element and another mold surface in the form of a shallow cone on another side of the heating element. The heating element has two heating units for keeping the two sides of the heating element on different temperatures. This heating element is intended for contact heating and thereby providing a respective shaping of the mating partners, namely the tuft carrier on one side and the tuft end on the other side.
It is an object of the present disclosure to provide a device and a method to fuse without contact the ends of thermoplastic filaments grouped to tufts that is improved over the prior art or that at least provides an alternative.